1. Field of Invention
The present invention relates to a direct type backlight. More particularly, the present invention relates to a distribution of light emitting diodes (LEDs) for the backlight.
2. Description of Related Art
The principle for operating a backlight module is to direct the light emitted from a backlight as a planar light source via a light guide plate, thereby assuring the uniformity of lightness. A backlight commonly used in the backlight module can be such as a cold cathode fluorescent lamp (CCFL) and light emitting diodes (LEDs), etc. Although the CCFL is the main trend currently, yet the demands for using the LEDs have been increasing daily. In comparison with the CCFL, the LEDs have the advantages of small size, long operation life, low driving voltage, low power consumption and excellent shock resistance, etc.
FIG. 1 is a schematic diagram showing a conventional direct type backlight using light emitting diodes, and the direct type backlight includes a plate 102 and several LED rows 104 disposed on the plate 102. Each of the LED rows 104 comprises several light emitting diodes 114, and row gaps a1, a2, a3 and a4 between two of the LED rows 104 are all the same, i.e. a1=a2=a3=a4.
The aforementioned light emitting diodes are evenly spaced on the plate according to a conventional distribution, i.e. the row gaps between any two adjacent LED rows 104 are all the same. However, this conventional distribution with equal gaps makes the central lightness of LED fail to achieve optimum application. Since user's visual sensation is mainly dependent on the central position of a panel, the lightness distribution obtained by this conventional distribution cannot optimize the user's visual sensation.